3D hydrodynamic investigation of thermal regime in a large river-lake-floodplain system (Poyang Lake, China)

Thermal regime and its response to meteorological and hydrological forcings play an important role in controlling water quality and ecosystem of lakes. Many large floodplain lakes are subjected to significant river-lake interactions and could benefit greatly from hydrodynamic modeling. The current work presents a first attempt to use a 3D hydrodynamic model and statistical methods to explore spatiotemporal variations and primary causal factors of thermal stability within a large river-lake-floodplain system (Poyang Lake, China). The hydrodynamic model successfully reproduced the lake hydrodynamics and thermal dynamics through a comparative analysis of field measurements. Simulation results revealed that the thermal stability of Poyang Lake exhibits similar spatial patterns between seasons; however, the lake is generally stratified during summer and early autumn. It is classified as partial mixed and full mixed during winter and spring. The thermal stratification may develop in the center area and eastern bay area of the lake, while the full mixing is likely to occur in the floodplains and the main flow channels. Statistics and simulations indicate that the air temperature, solar radiation and evaporation trigger a positive effect on the thermal stability of Poyang Lake, whereas a negative relationship is recognized due to the catchment river temperature. The responses of thermal stability to the meteorological and hydrological changes are much stronger in summer than other seasons, producing a significant seasonal thermal regime in the floodplain lake. Additionally, the dynamics in the lake water depth and associated hydrological regime are a major factor in maintaining the seasonal thermal stability of Poyang Lake. The findings of this study can support management of Poyang Lake as well as other similar floodplain lakes, by providing information on both water quality and ecosystem succession.